The active matrix panel display elements possess many merits of thin frame, power saving, no radiation, etc. and have been widely used. In the present market, the flat panel display comprises Liquid Crystal Displays (LCD) and Organic Light Emitting Diodes (OLED).
The LCD comprises a liquid crystal display panel and a backlight module. The working principle of the liquid crystal display panel is to locate liquid crystal molecules between two parallel glass substrates. The light of back light module is reflected to generate images by applying driving voltages to control whether the liquid crystal molecules to be changed directions.
An OLED possesses properties of self-illumination, high brightness, wide view angle, high contrast, flexibility and low power consumption, etc., and accordingly has been received more attentions. As being the display of next generation, it has been gradually replaced traditional liquid crystal displays and widely applied in cellular phone screens, computer displays, full color TV, etc. OLED display technology is different from the traditional liquid crystal display technology and the back light is not required. It utilizes an ultra thin organic material coating layer and a glass substrate, and theses organic material will illuminate when the current is conducted.
The thin film transistor array substrate has been widely applied in LCD and OLED, which generally comprises a glass substrate and a thin film transistor and a storage capacitor formed on the glass substrate.
The storage capacitor plays a role having the important functions of maintaining voltage level, reducing the coupling capacitor dividing voltage. Generally, we prefer a larger capacitance. The calculation of the capacitance is C=εS/D, wherein S represents the area, and D represents the isolation layer thickness. To change the value of the storage capacitor, several methods are listed, of which the first one is selecting an isolation material with a larger dielectric constant the second one is increasing the area; and the third one is reducing the isolation layer thickness.
Generally, enlarging the relative area of the two metal plates will increase the capacitance. However, the storage capacitor is commonly manufactured by clamping the isolation layer. The metal electrode is opaque. The larger the storage capacitor is, the lower the aperture ratio becomes. Reducing the isolation layer thickness can increase the value of the storage capacitor, and on this basis, the relative area of the metal plates can be properly reduced, which is a better method of increasing the storage capacitor and raising the aperture ratio.
Referring to FIG. 1, a sectional view is provided to illustrate a known thin film transistor array substrate, which comprises a substrate 100, and a thin film transistor and a storage capacitor formed on the substrate 100. The first electrode plate 310 and the second electrode plate 320 of the storage capacitor clamp the gate isolation layer 300 and the etching stopper layer 500 in-between. Because both the gate isolation layer 300 and the etching stopper layer 500 possess a certain thickness, which makes that the isolation layer is thicker and the storage capacitance is smaller. A larger relative area is required for obtaining a desired capacitance value. Therefore, the element aperture ratio is reduced.